Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/github.com/json-iterator/go/pool.go

@@ -0,0 +1,42 @@
+package jsoniter
+
+import (
+	"io"
+)
+
+// IteratorPool a thread safe pool of iterators with same configuration
+type IteratorPool interface {
+	BorrowIterator(data []byte) *Iterator
+	ReturnIterator(iter *Iterator)
+}
+
+// StreamPool a thread safe pool of streams with same configuration
+type StreamPool interface {
+	BorrowStream(writer io.Writer) *Stream
+	ReturnStream(stream *Stream)
+}
+
+func (cfg *frozenConfig) BorrowStream(writer io.Writer) *Stream {
+	stream := cfg.streamPool.Get().(*Stream)
+	stream.Reset(writer)
+	return stream
+}
+
+func (cfg *frozenConfig) ReturnStream(stream *Stream) {
+	stream.out = nil
+	stream.Error = nil
+	stream.Attachment = nil
+	cfg.streamPool.Put(stream)
+}
+
+func (cfg *frozenConfig) BorrowIterator(data []byte) *Iterator {
+	iter := cfg.iteratorPool.Get().(*Iterator)
+	iter.ResetBytes(data)
+	return iter
+}
+
+func (cfg *frozenConfig) ReturnIterator(iter *Iterator) {
+	iter.Error = nil
+	iter.Attachment = nil
+	cfg.iteratorPool.Put(iter)
+}